For this novel, Sayers had to learn about change ringing. In it, Lord Peter not only rings one of eight church bells in a record-setting series of sound patterns called "changes", but also uses his knowledge of bell-ringing to solve a 20-year-old mystery, located in the Fens, involving a stolen emerald necklace.
The title refers to the ringing of a church bell to signal a death in the parish. There is a ring of eight bells at the local church, each with its own name and history. The largest, the tenor bell, is Tailor Paul, the great bell on which are rung nine “tailor” or “teller” strokes at the death of a man in the parish, and six at the death of a woman. One stroke then follows for every year of the deceased’s life.
Stranded in a Fenland village on New Year’s Eve after a car accident, Wimsey helps ring a nine-hour peal of bells overnight after Will Thoday, one of the ringers, is stricken by influenza. Lady Thorpe, wife of Sir Henry Thorpe, the local squire, dies next morning and Wimsey hears how the Thorpe family has been blighted for 20 years by the unsolved theft of jewels from a house-guest by the butler, Deacon, and an accomplice, Cranton.
At Easter, Sir Henry himself dies and his wife's grave is opened for his burial. A body is found hidden in the grave, mutilated beyond recognition. It is first thought to be the body of one Driver, a tramp labourer who arrived and then vanished just after the New Year. However, an odd cipher found in the bell-chamber suggests a link with France, and the dead man is found to be Cobbleigh, a British soldier who deserted and stayed in France after the war. Cobbleigh appears to have discovered where the emeralds were hidden, and then to have plotted to recover them, probably with "Driver". "Driver" is discovered to be an alias of Cranton, the accomplice in the original theft.
Wimsey assumes the two men did recover the emeralds and Cranton then killed Cobbleigh for them, but cannot prove it. However, when he decodes the cipher (which requires knowledge of change-ringing) it leads him to the emeralds, still untouched in their hiding place in the church.
Much becomes clear when Cobbleigh turns out to have been Deacon, the thieving butler. Imprisoned along with Cranton for the theft, he murdered a warder and escaped. A body, apparently his, was later found, but in fact Deacon had murdered a soldier and swapped identities with him. He married (bigamously, of course) in France and waited years to return for the emeralds, which he had hidden before his arrest. Since he risked hanging if caught, he finally asked Cranton to help, sending him the cipher as a clue to the hiding place as a token of good faith. Cranton could not solve it but knew it related to the bells, so he came to Fenchurch as “Driver” on New Year’s Day. He went to the bell-chamber on the night of 4 January, but found Deacon‘s dead, bound body in the chamber and fled, dropping the cipher. There is still no clue as to how Deacon died.
Wimsey uncovers the truth. Deacon came to the church on 30 December to get the emeralds and encountered Will Thoday. Thoday had married Deacon's English wife Mary after the war, believing her a widow. Now he realised Deacon was still alive, making his and Mary's marriage bigamous and their daughters illegitimate. Desperate to prevent Deacon raking up the past and exposing his family to pain and scandal, Thoday tied him up in the bell-chamber, planning to bribe him to leave. But he became helpless with influenza next day (which is why Wimsey rang his bell in the New Year peal). Will’s sailor brother Jim eventually found Deacon dead in the bell-chamber on 2 January and assumed Will had murdered him. Appalled but loyal, he waited until Lady Thorpe’s funeral on 4 January, made the body unrecognisable and hid it in the new grave, then left for sea. When the body was discovered, Will assumed Jim had killed Deacon. Neither can explain how Deacon died.
The mystery is almost over; Deacon’s death alone remains inexplicable. It is only when Wimsey returns to Fenchurch the following Christmas that he understands. Floods inundate the countryside, and Wimsey climbs the tower as the bells are ringing the alarm. The appalling noise in the bell-chamber convinces him that Deacon, tied there for hours between New Year’s Eve and New Year’s Day when Wimsey helped with the all-night peal, could not have survived. Deacon was killed by the ringers - or by the bells themselves.
"For many reasons, no great favourite ... despite Dorothy's swotting up of bell-ringing and the two good maps. The cause of death, however, is original, and the rescue scene in the church amid the flood shows the hand of the master. It should be added that this work is a favorite with many readers. Sinclair Lewis judged it the best of his four "indispensables" ...".
"Dorothy L. Sayers incautiously entered the closed world of bell-ringing in The Nine Tailors on the strength of a sixpenny pamphlet picked up by chance -- and invented a method of killing which would not produce death, as well as breaking a fundamental rule of that esoteric art by allowing a relief ringer to take part in her famous nine-hour champion peal.
In his infamous essay attacking detective fiction, Who Cares Who Killed Roger Ackroyd, American critic Edmund Wilson decried this novels as dull, overlong and far too detailed; describing how he skipped a lot of the prose about bell-ringing (quote: "a lot of information of the kind that you might expect to find in an encyclopaedia article on campanology"), and also large amounts of Sayers’ focal sleuth character, "the embarrassingly named" Lord Peter Wimsey.
Hilary Thorpe, the resourceful and independent-minded 15-year old daughter of Sir Henry Thorpe - who bravely faces the loss of both parents during the book, and who provided vital help to Wimsey in solving the mystery - is mentioned as intending to become a writer and to study at Oxford, both being unconventional ambitions for a woman at the time of writing, and both based on the writer's own life.